This invention relates to the regioselective synthesis of derivatives of rapamycin at the 42-position, which are useful for inducing immunosuppression, and in the treatment of transplantation rejection, graft vs. host disease, autoimmune diseases, diseases of inflammation, adult T-cell leukemia/lymphoma, solid tumors, fungal infections, and hyperproliferative vascular disorders.
Rapamycin is a macrocyclic triene antibiotic produced by Streptomyces hygroscopicus, which was found to have antifungal activity, particularly against Candida albicans, both in vitro and in vivo [C. Vezina et al., J. Antibiot. 28, 721 (1975); S. N. Sehgal et al., J. Antibiot. 28, 727 (1975); H. A. Baker et al., J. Antibiot. 31, 539 (1978); U.S. Pat. No. 3,929,992; and U.S. Pat. No. 3,993,749].
Rapamycin alone (U.S. Pat. No. 4,885,171) or in combination with picibanil (U.S. Pat. No. 4,401,653) has been shown to have antitumor activity. R. Martel et al. [Can. J. Physiol. Pharmacol. 55, 48 (1977)] disclosed that rapamycin is effective in the experimental allergic encephalomyelitis model, a model for multiple sclerosis; in the adjuvant arthritis model, a model for rheumatoid arthritis; and effectively inhibited the formation of IgE-like antibodies.
The immunosuppressive effects of rapamycin have been disclosed in FASEB 3, 3411 (1989). Cyclosporin A and FK-506, other macrocyclic molecules, also have been shown to be effective as immunosuppressive agents, therefore useful in preventing transplant rejection [FASEB 3, 3411 (1989); FASEB 3, 5256 (1989); R. Y. Calne et al., Lancet 1183 (1978); and U.S. Pat. No. 5,100,899].
Rapamycin has also been shown to be useful in preventing or treating systemic lupus erythematosus [U.S. Pat. No. 5,078,999], pulmonary inflammation [U.S. Pat. No. 5,080,899], insulin dependent diabetes mellitus [U.S. Pat. No. 5,321,009], smooth muscle cell proliferation and intimal thickening following vascular injury [U.S. Pat. No. 5,516,781], adult T-cell leukemia/lymphoma [European Patent Application 525,960 A1], and ocular inflammation [U.S. Pat. No. 5,387,589].
Numerous rapamycin 42-derivatives are known, typically being esters (carbon and sulfur based) or ethers of the 42-hydroxyl group of rapamycin, that are produced by esterification or etherification of the 42-position. Esterification of rapamycin at the 42-position was commonly prepared by directly reacting rapamycin with acylating agents in order to afford the desired product. The chemistry appeared to be rather simple. However, as rapamycin contains two secondary hydroxyl groups at positions 31 and 42, attempts to discriminate between these two functional centers in order to achieve a selective synthesis of 42-monoacylated product, posed a difficult challenge. This type of non-regioselective reaction also produced a 31,42-bis-acylated by-product and as well, some unreacted rapamycin remained in the reaction mixture. The final result was a lower yield that required extensive purification to obtain pure 42-monoacylated product.